This invention relates to rare earth garnets, and more particularly relates to such garnets having a metallized bonding surface, and garnet to metal seals formed with this surface.
Rare earth garnets such as yttrium aluminum garnet (YAG) and yttrium indium garnet (YIG) exhibit unique optical and magnetic properties which make these materials useful in a variety of applications, such as magnetic bubble domain memory devices; magnetooptic devices, e.g., modulators, optic devices, e.g., lasers; and microwave devices, e.g., circulators. Often, the desired properties reside in an epitaxial single crystal layer supported on a polycrystalline substrate, and are achieved by complex substitutions of constituents into the garnet crystal structure.
The need to mount such devices to metal substrates such as walls or brackets presents a unique bonding problem. In addition to the known incompatibility between oxide and metal surfaces, the garnets themselves are often mechanically or chemically fragile. For example, in one application, the garnet is rectangular in shape, having an aspect ratio of about 6 to 1, thus giving rise to significant stresses due to differential thermal expansion in the body during heating. In addition, heating to temperatures above 400.degree. C., necessary for most brazing operations, even for a short time, may cause irreversible changes in the magnetic or optical properties, especially of the thin epitaxial layer.
In U.S. Pat. No. 3,969,086, a garnet is metallized for bonding by sputter depositing a nichrome, molybdenum or chromium layer on the garnet, followed by a copper layer, and then a gold layer. The gold layer is then soldered to the metal to be bonded.
In U.S. Pat. No. 4,210,389, a YAG laser is first metallized with a sputtered reflective layer of aluminum, gold, silver or rhodium. This layer is then covered with a sputtered layer of either nichrome, titanium or tungsten, followed by a sputtered layer of gold or platinum. This gold or platinum layer is then soldered to a copper mount metallized with gold or platinum.
While the above structures apparently provide adequate garnet to metal seals, it is desirable to develop highly adherent, relatively cheap seals which do not rely upon the use of one or more precious metal layers.
Accordingly, it is an object of the invention to provide a metallized garnet suitable for soldering or brazing to a metal, the metallization for which is highly adherent to the garnet substrate and does not contain precious metals.